When a payment terminal reads a card and transmits payment data to a server, the server approves the payment and provides the approval result to the payment terminal. When a plurality of payment terminals simultaneously reads a plurality of cards and transmits data, the server requires a lot of time to process the data, and the processing load is high. In particular, when a failure occurs on a communication line between the server and the payment terminals, the processing load of the server accumulates. In this case, an inquiry about a transaction history and transmission of a response to the inquiry may not be smoothly performed.